Develop, using chromosome instability (chromosome breakage and sister chromatid exchange) as the end-point, methods for the detection of the heterozygous genotypes for the genes causing the autosomal recessive disorders Fanconi's anemia. In addition, other syndromes such as AT, XP, may be tested as a correlate; however, the primary focus will be to determine a methodology which will detect heterozygote genotypes of FA.